Some mention of nudity though the nudity is always implied and rarely if ever shown. There are also references to sexual orientation and humor around character's sexual orientation. Additionally, there are several sexual jokes throughout the show. However, references to sex, sexuality, nudity are never explicit.
Season two, episode 10 (Christmas) Meredith flashes Michael for about two seconds, then he runs away. Implying that she is drunk.
season two, episode 13, Jim and Michael go to hooters, women are shown in scantily clad outfits.
Season three, episode one ("Gay Witch Hunt"): Michael kisses Oscar in a conference room. This episode also has a LOT of gay humor.
The character, Oscar, turns out to be gay. There are some gay jokes and other stuff, but it is hardly ever mentioned.
Season three, episode 12 ("Ben Franklin"): a stripper is hired in a warehouse. Fully clothed, she sits on another person's lap, starts dancing a little bit, and then rips off her shirt to reveal her bra and midriff -- which can be seen for about four to five seconds. Not a very suggestive scene, and is meant to be humorous in an awkward way.
Michael fondles Jan's clothed breasts for about 10 seconds in the season three finale ("The Job").
Two characters come close to basically having a legal prostitution-like contract. No sexual action is shown.
Season four, episode 14 ("Goodbye, Toby") contains the only instance of a sex scene being shown and not implied. Still, this is brief with no nudity. We only see a bare back and shoulders.
Season six, episode 18 ("The Delivery, Part 2"): A married couple worries about whether or not their baby is breastfeeding correctly. A lactation consultant comes in and puts his hand up the wife's shirt to make sure nothing is wrong. This makes the husband uncomfortable since the consultant is a male. Mainly comedic.
In season seven, episode five ("Sex Ed"), Andy is a sexual education instructor. In the conference room, there are many lines of dialogue about STDs, impotence, and erections in this episode.
Season eight, episode 12 ("Pool Party"): three men prepare to skinny dip and their backsides are seen, although their buttocks are all blurred.
Season eight, episode 20 ("Angry Andy"): Andy fails to perform sexually and there is an entire office meeting discussing impotence. This includes references to "satisfaction" and ejaculation and is pretty explicit, even in comparison to Todd Packer episodes.
Season nine, episode eight ("The Target"): an instance of Dwight's entire naked body onscreen with his penis blurred out.
Season nine, episode 15 ("Moving On"): the F-word is about to be used with its sexual meaning but the character stops himself saying "you [two] were fuu-uuhhh ahhh!"
One male says "Let's talk about penis diseases, how about you." He points towards a female and she says "I don't have a penis, I have a vagina." Meant for laughs.
Although sexual references to oral or anal sex are never explicitly stated, and they are usually somewhat cryptic and subtle double-entendre references, there is one episode in which Michael explicitly talks about oral sex as having a "penis in your mouth." This is perhaps the most explicitly-stated crude content in the show.
Overall, while there is a lot of sexual content in this show, all nudity is suggested and covered by sensor techniques. Also, a lot of the sexual jokes are not supposed to be accepted, and often the characters are appalled at one character in particular's language.